Hyperbranched polymers structural characterization

Often in hyperbranched polymers obtained via SCVP, it is not possible to determine the DB directly via NMR analysis. Therefore, other methods, for example, viscosity measurements and light-scattering methods have to be used to confirm the compact structure of a hyperbranched polymer. Such characterizations of hyperbranched (meth)acrylates will be discussed in the next section. 

AB2 reacts selectively with only one antagonist function of a second polyfunctional molecule, the other ones being protected81 (Fig. 5.16). The perfect hyperbranched molecules obtained according to that step-by-step process are called dendrimers. The degree of branching characterizes the structure of a hyperbranched polymer and has been defined by Hawker et al.82 as... 

In this context numerous changes were made. The chapter Properties of Polymers was revised and a new section Correlations of Structure and Morphology with the Properties of Polymers was added. The chapter Characterization of Macromolecules was revised and enlarged. 15 examples have been deleted as they did no longer represent the state of the art and/or were of minor educational value. Several new experiments (plus background text) were added, as, for example controlled radical polymerization - enzymatic polymerization - microemulsions - polyelectrolytes as superabsorbants - hyperbranched polymers - new blockcopolymers - high impact polystyrene - electrical conducting polymers. 

In the beginning, the term dendrimer , which was established by Tomalia in 1985 [42,43], described all types of dendritic polymers. Later a distinction based on the relative degree of structural control present in the architecture was drawn. Nowadays, many other types of dendritic architectures are known, even if most of them, however, have not yet been widely investigated and fully characterized. The term dendritic polymer involves four substructures (Fig. 2), namely dendrimers themselves, dendrons, random hyperbranched polymers, and dendrigraft polymers [44, 45],... 

Whereas the well-characterized, perfect (or nearly so) structures of dendritic macromolecules, constructed in discrete stepwise procedures have been described in the preceding chapters, this Chapter reports on the related, less than perfect, hyperbranched polymers, which are synthesized by means of a direct, one-step polycondensation of A B monomers, where x > 2. Flory s prediction and subsequent demonstration 1,2 that A B monomers generate highly branched polymers heralded advances in the creation of idealized dendritic systems thus the desire for simpler, and in most cases more economical, (one-step) procedures to the hyperbranched relatives became more attractive. 

Additional studies have focused on the structure, modification and characterization of hyperbranched poly(carbosilanes) synthesized via hydrosilylation. The structure of the hyperbranched polymer derived from methyldiallylsilane was examined using small-angle... 

Precisely branched polymers include hyperbranched polymers, dendrimers and den-drons. Dendrimers and dendrons are characterized by perfectly controlled structures in three dimensions such as tree branch architecture, and they have attractive features such as a well-ordered chemical structure, molecular mass, size and configuration of polymers [5], Although the precise order of shape of hyperbranched polymers is less than that of dendrimers and dendrons, hyperbranched polymers have unique properties such as low viscosity attributed to the lack of entanglanent of polymer segments, and the possibility of chemical modification in terminal functional groups such as in dendrimers [1-3]. 

Ihe literature " describes a number of dendrimers and the closely related star-like 120-123 polysiloxanes. Ihe hyperbranched polysiloxanes are the primary example of more random structures. Although the emphasis has been on synthesis and characterization,i i modeling on hyperbranched polymers has also been carried out. Some of the most interesting species involve polysiloxane chains. Star polymers, some with nanosized silica cores, have also been synthesized.i °-i i Hyperbranched polysiloxanes have been prepared with controllable molecular weights and polydispersities,i -1 - with epoxy terminal groups some are UV-curable ° and some serve as a source of molecular silica. Hyperbranched polysiloxanes have also been used in the sol-gel preparation of polypropylene/silica nanocomposites. ... 

In this chapter we consider the properties of synthetic polymers. First, the main techniques of polymer synthesis are outlined (Section 2.2). Then the conformation of polymer molecules is discussed in Section 2.3. We move on to a summary of the main methods for characterization of polymeric materials in Section 2.4. Then the distinct features of the main classes of polymer are considered, i.e. solutions (Section 2.5), melts (and glasses) (Section 2.6) and crystals (Section 2.7). Then the important properties of plastics (Section 2.8), rubber (Section 2.9) and polymer fibres (Section 2.10) are related to microscopic structure and to rheology. Polymer blends and block copolymers form varied structures due to phase separation, and this is compared and contrasted for the two types of system in Section 2.11. Section 2.12 is concerned with dendrimers and hyperbranched polymers. Section 2.13 and 2.14 deal with polyelectrolytes and (opto)electronic polymers respectively. 

GC alone can be a valuable monomer for the synthesis of hyperbranched poly(hydroxyether)s (Scheme 25). In case of polymerization, GC, containing a l,3-dioxolan-2-one ring and hydroxyl group in a single molecule, is considered a latent cyclic AB2-type monomer. The anionic ROP of the GC, which proceeds with CO2 liberation, leads to a branched polyether. l,l,l-Tris(hydroxymethyl)propane or other multihydroxyl molecules are usually used as a initiator-starter and central core of the polyether. The hyperbranched polyglycerol structure is obtained by slow addition of the cyclic carbonate monomer at above 150 °C. Such polymers are characterized by a flexible polyether core and a multihydroxyl outer sphere. They are suitable for preparation of acrylic resins for dental applications or additives for polyurethane foams. Hyperbranched poly (hydroxyether)s from biscyclic carbonate with phenol group (2, Scheme 24) were also reported. 

---